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net: tcp: split ack slow/fast events from cwnd_event 

The congestion control ops "cwnd_event" currently supports
CA_EVENT_FAST_ACK and CA_EVENT_SLOW_ACK events (among others).
Both FAST and SLOW_ACK are only used by Westwood congestion
control algorithm.

This removes both flags from cwnd_event and adds a new
in_ack_event callback for this. The goal is to be able to
provide more detailed information about ACKs, such as whether
ECE flag was set, or whether the ACK resulted in a window
update.

It is required for DataCenter TCP (DCTCP) congestion control
algorithm as it makes a different choice depending on ECE being
set or not.

Joint work with Daniel Borkmann and Glenn Judd.

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: Glenn Judd <glenn.judd@morganstanley.com>
Acked-by: Stephen Hemminger <stephen@networkplumber.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Florian Westphal 2014-09-26 22:37:34 +02:00 committed by David S. Miller
parent 30e502a34b
commit 7354c8c389
3 changed files with 32 additions and 16 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
include/net/tcp.h
View File

@ -763,8 +763,10 @@ enum tcp_ca_event {
CA_EVENT_CWND_RESTART, /* congestion window restart */
CA_EVENT_COMPLETE_CWR, /* end of congestion recovery */
CA_EVENT_LOSS, /* loss timeout */
CA_EVENT_FAST_ACK, /* in sequence ack */
CA_EVENT_SLOW_ACK, /* other ack */
};
enum tcp_ca_ack_event_flags {
CA_ACK_SLOWPATH = (1 << 0),
};
/*
@ -796,6 +798,8 @@ struct tcp_congestion_ops {
void (*set_state)(struct sock *sk, u8 new_state);
/* call when cwnd event occurs (optional) */
void (*cwnd_event)(struct sock *sk, enum tcp_ca_event ev);
/* call when ack arrives (optional) */
void (*in_ack_event)(struct sock *sk, u32 flags);
/* new value of cwnd after loss (optional) */
u32 (*undo_cwnd)(struct sock *sk);
/* hook for packet ack accounting (optional) */

12
net/ipv4/tcp_input.c
View File

@ -3362,6 +3362,14 @@ static void tcp_process_tlp_ack(struct sock *sk, u32 ack, int flag)
}
}
static inline void tcp_in_ack_event(struct sock *sk, u32 flags)
{
const struct inet_connection_sock *icsk = inet_csk(sk);
if (icsk->icsk_ca_ops->in_ack_event)
icsk->icsk_ca_ops->in_ack_event(sk, flags);
}
/* This routine deals with incoming acks, but not outgoing ones. */
static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
{
@ -3421,7 +3429,7 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
tp->snd_una = ack;
flag |= FLAG_WIN_UPDATE;
tcp_ca_event(sk, CA_EVENT_FAST_ACK);
tcp_in_ack_event(sk, 0);
NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPHPACKS);
} else {
@ -3439,7 +3447,7 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
if (TCP_ECN_rcv_ecn_echo(tp, tcp_hdr(skb)))
flag |= FLAG_ECE;
tcp_ca_event(sk, CA_EVENT_SLOW_ACK);
tcp_in_ack_event(sk, CA_ACK_SLOWPATH);
}
/* We passed data and got it acked, remove any soft error

28
net/ipv4/tcp_westwood.c
View File

@ -220,32 +220,35 @@ static u32 tcp_westwood_bw_rttmin(const struct sock *sk)
return max_t(u32, (w->bw_est * w->rtt_min) / tp->mss_cache, 2);
}
static void tcp_westwood_ack(struct sock *sk, u32 ack_flags)
{
if (ack_flags & CA_ACK_SLOWPATH) {
struct westwood *w = inet_csk_ca(sk);
westwood_update_window(sk);
w->bk += westwood_acked_count(sk);
update_rtt_min(w);
return;
}
westwood_fast_bw(sk);
}
static void tcp_westwood_event(struct sock *sk, enum tcp_ca_event event)
{
struct tcp_sock *tp = tcp_sk(sk);
struct westwood *w = inet_csk_ca(sk);
switch (event) {
case CA_EVENT_FAST_ACK:
westwood_fast_bw(sk);
break;
case CA_EVENT_COMPLETE_CWR:
tp->snd_cwnd = tp->snd_ssthresh = tcp_westwood_bw_rttmin(sk);
break;
case CA_EVENT_LOSS:
tp->snd_ssthresh = tcp_westwood_bw_rttmin(sk);
/* Update RTT_min when next ack arrives */
w->reset_rtt_min = 1;
break;
case CA_EVENT_SLOW_ACK:
westwood_update_window(sk);
w->bk += westwood_acked_count(sk);
update_rtt_min(w);
break;
default:
/* don't care */
break;
@ -274,6 +277,7 @@ static struct tcp_congestion_ops tcp_westwood __read_mostly = {
.ssthresh = tcp_reno_ssthresh,
.cong_avoid = tcp_reno_cong_avoid,
.cwnd_event = tcp_westwood_event,
.in_ack_event = tcp_westwood_ack,
.get_info = tcp_westwood_info,
.pkts_acked = tcp_westwood_pkts_acked,